Formation Scenario for Wide and Close Binary Systems

Machida, Masahiro N.; Tomisaka, Kohji; Matsumoto, Toshiro; Inutsuka, S.

doi:10.1086/529133

Cited by 131 publications

(162 citation statements)

References 77 publications

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“…When α = 90 • , we find that disks may form for smaller values of μ, as long as μ > 2−3, and for even lower values of μ, disk formation does not seem to be possible. Nevertheless, for these highly magnetized configurations, the question of whether a disk may form at later times, or because of non-ideal MHD effects (Hosking & Whitworth 2004;Machida et al 2008;Mellon & Li 2009), remains unanswered. We recall that although Belloche et al (2002) observe a significant amount of rotation in the envelope of IRAM04191, they exclude a disk of size larger than 20 AU.…”

Section: Resultsmentioning

confidence: 99%

Disk formation during collapse of magnetized protostellar cores

Hennebelle¹,

Ciardi

2009

A&A

223

255

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Context. In the context of star and planet formation, understanding the formation of disks is of fundamental importance. Aims. Previous studies found that the magnetic field has a very strong impact on the collapse of a prestellar cloud, by possibly suppressing the formation of a disk even for relatively modest values of the magnetic intensity. Since observations infer that cores have a substantial level of magnetization, this raises the question of how disks form. However, most studies have been restricted to the case in which the initial angle, α, between the magnetic field and the rotation axis equals 0 • . Here we explore and analyse the influence of non aligned configurations on disk formation. Methods. We perform 3D ideal MHD, AMR numerical simulations for various values of μ, the ratio of the mass-to-flux to the critical mass-to-flux, and various values of α. Results. We find that disks form more easily as α increases from 0 to 90 • . We propose that as the magnetized pseudo-disks become thicker with increasing α, the magnetic braking efficiency is lowered. We also find that even small values of α ( 10-20 • ) show significant differences with the aligned case. Conclusions. Within the framework of ideal MHD, and for our choice of initial conditions, centrifugally supported disks cannot form for values of μ smaller than 3 when the magnetic field and the rotation axis are perpendicular, and smaller than about 5-10 when they are perfectly aligned.

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Section: Resultsmentioning

confidence: 99%

Disk formation during collapse of magnetized protostellar cores

Hennebelle¹,

Ciardi

2009

A&A

223

255

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“…Few studies have explored the influence of non ideal MHD effects. Machida et al (2008) include ohmic dissipation and find that binaries may form during the second collapse, while Duffin & Pudritz (2009) consider ambipolar diffusion and find that in a highly rotating case, two fragments instead of one form when ambipolar diffusion is included.…”

Section: Introductionmentioning

confidence: 99%

Collapse, outflows and fragmentation of massive, turbulent and magnetized prestellar barotropic cores

Hennebelle

Commerçon

Joos

et al. 2011

A&A

188

216

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Context. Stars, and more particularly massive stars, have a drastic impact on galaxy evolution. Yet the conditions in which they form and collapse are still not fully understood. Aims. In particular, the influence of the magnetic field on the collapse of massive clumps is relatively unexplored, it is therefore of great relevance in the context of the formation of massive stars to investigate its impact. Methods. We perform high resolution, MHD simulations of the collapse of one hundred solar masses, turbulent and magnetized clouds, with the adaptive mesh refinement code RAMSES. We compute various quantities such as mass distribution, magnetic field, and angular momentum within the collapsing core and study the episodic outflows and the fragmentation that occurs during the collapse. Results. The magnetic field has a drastic impact on the cloud evolution. We find that magnetic braking is able to substantially reduce the angular momentum in the inner part of the collapsing cloud. Fast and episodic outflows are being launched with typical velocities of the order of 1−3 km s −1 , although the highest velocities can be as high as 20−40 km s −1 . The fragmentation in several objects is reduced in substantially magnetized clouds with respect to hydrodynamical ones by a factor of the order of 1.5−2. Conclusions. We conclude that magnetic fields have a significant impact on the evolution of massive clumps. In combination with radiation, magnetic fields largely determine the outcome of massive core collapse. We stress that numerical convergence of MHD collapse is a challenging issue. In particular, numerical diffusion appears to be important at high density and therefore could possibly lead to an overestimation of the number of fragments.

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“…These new MHD simulations indicate that the presence of an even moderate magnetic field strongly modifies angular momentum transport during collapse and at least partly suppresses core fragmentation, often leading to the formation of a single object. Price & Bate (2007) and conclude that binary star formation is still possible in the presence of magnetic fields but either requires strong initial perturbations or must occur during the second collapse phase, after the dissociation of H 2 (Machida et al 2008). The systems formed in the latter case are initially very-low-mass (∼0.01 M ), close (∼1 AU) binaries (Bonnell & Bate 1994), which have to grow substantially by accretion during the Class 0/Class I phase (Bate 2000) to match the properties of observed young binary stars (e.g.…”

Section: Introductionmentioning

confidence: 99%

Toward understanding the formation of multiple systems

Maury¹,

André²,

Hennebelle

et al. 2010

A&A

156

230

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Context. The formation process of binary stars and multiple systems is poorly understood. The multiplicity rate of Class II premain-sequence stars and Class I protostars is well documented and known to be high (∼ 30% to 50% between ∼100 and 4000 AU). However, optical / near-infrared observations of Class I/Class II YSOs barely constrain the pristine properties of multiple systems, since dynamical evolution can quickly alter these properties during the protostellar phase. Aims. Here, we seek to determine the typical outcome of protostellar collapse and to constrain models of binary formation by core fragmentation during collapse, using high-resolution millimeter continuum imaging of very young (Class 0) protostars observed at the beginning of the main accretion phase. Methods. We carried out a pilot high-resolution study of 5 Class 0 objects, including 3 Taurus sources and 2 Perseus sources, using the most extended (A) configuration of the IRAM Plateau de Bure Interferometer (PdBI) at 1.3 mm. Our PdBI observations have a typical HPBW resolution ∼0.3 −0.5 and rms continuum sensitivity ∼0.1−1 mJy/beam, which allow us to probe the multiplicity of Class 0 protostars down to separations a ∼ 50 AU and circumstellar mass ratios q ∼ 0.07. Results. We detected all 5 primary Class 0 sources in the 1.3 mm dust continuum. A single component associated with the primary Class 0 object was detected in the case of the three Taurus sources, while robust evidence of secondary components was found toward the two Perseus sources: L1448-C and NGC1333-IR2A. We show that the secondary 1.3 mm continuum component detected ∼600 AU south-east of L1448-C, at a position angle close to that of the CO(2−1) jet axis traced by our data, is an outflow feature directly associated with the powerful jet driven by L1448-C. The secondary 1.3 mm continuum component detected ∼1900 AU southeast of NGC1333-IR2A may either be a genuine protostellar companion or trace the edge of an outflow cavity. Therefore, our PdBI observations revealed only wide (>1500 AU) protobinary systems and/or outflow-generated features. Conclusions. When combined with previous millimeter interferometric observations of Class 0 protostars, our pilot PdBI study tentatively suggests that the binary fraction in the ∼75−1000 AU range increases from the Class 0 to the Class I stage. It also seems to argue against purely hydrodynamic models of binary star formation. We briefly discuss possible alternative scenarios to reconcile the low multiplicity rate of Class 0 protostars on small scales with the higher binary fraction observed at later (e.g. Class I) evolutionary stages.

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Formation Scenario for Wide and Close Binary Systems

Cited by 131 publications

References 77 publications

Disk formation during collapse of magnetized protostellar cores

Disk formation during collapse of magnetized protostellar cores

Collapse, outflows and fragmentation of massive, turbulent and magnetized prestellar barotropic cores

Toward understanding the formation of multiple systems

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